1. Field of the Invention
The present invention relates to an arrangement for controlling individual zones of a hot plate which is employed in the fabrication of semi-conductor devices.
In present installations, hot plate temperature control is generally based upon a relatively small number of sensors; for instance, normally about two sensors, which are buried within the hot plate, and no measures are provided which will enable to locally correct or adjust the temperature of the hot plate at a single sensor. Consequently, when the encountered degree of temperature uniformity deviates so as to be out of bounds of the required specification, the airflow within the enclosed hot plate environment may be tuned or modified as necessary in order to achieve an improved hot plate surface temperature uniformity. Moreover, a test wafer used in photolithographic processes having thermocouples and wire connections may be utilized to test hot plate surface temperatures and compare these with a standard; however, the wire connections tend to impact normal airflow, and resultingly it is not readily possible to achieve an ideal or true indication of hot plate surface or surface zone temperatures and uniformity across the surface of the hot plate.
2. Discussion of the Prior Art
Various publications are known with regard to different aspects directed to the controlling of the surface temperatures of hot plates, such as are used in the production of integrated circuit devices.
Schilling, et al., U.S. Pat. No. 5,396,047 discloses an electrical heating unit having peripherally extending surface areas with a plurality of radially spaced heating coils which are alternately heated. The heating coils have heat sensors embedded therein in order to provide a thermal profile which will facilitate switching over of the heating between the peripheral or annular heat coils in order to achieve a predetermined temperature pattern across the surface areas of the heating unit.
Carman, et al., U.S. Pat. No. 5,294,778 pertains to a wafer support platen incorporating a heating system for low pressure chemical vapor deposition, and wherein a plurality of circumferentially arranged resistance heaters incorporate sensors for an indication of specific temperatures at spots or point locations which are distributed across the surface of the hot plate. Responsive to predetermined temperature requirements or temperature deviations, as may be the specific case, an appropriate electrical current may be imparted to the various resistance heaters through the intermediary of a temperature controller to provide the desired surface temperature for the hot plate which is employed for the support of a wafer for an integrated circuit device.
Higgins, et al., U.S. Pat. No. 4,918,291 discloses an electrical heater assembly construction including a glass ceramic top cooking plate in which embedded electrical heating elements are adapted to have their temperatures regulated through the intermediary of a suitable temperature controller system. The different electrical power supply levels for the heating elements can be controlled by an energy regulator or an electronic phase control.
Liao, et al., U.S. Pat. No. 5,702,624 pertains to a hot plate temperature control system for the heat treatment of wafers having integrated circuits thereon through the curing of photoresist which is deposited on a semiconductor substrate. Suitable thermocouples may be arranged in physical connection with a hot plate supporting the wafers so as to sense variations in the temperatures within particular hot plates surface zones, enabling a power monitor and controller to regulate the temperatures in order to achieve desired temperature conditions within the hot plate and across the various surface zones thereof, as may be required by specified production conditions.
IBM Technical Disclosure Bulletin, Vol. 34, No. 5, October 1991, pgs. 350 through 353, describes wavelength modulated interferometric thermometry for the measurement of non-monotonic temperature changes. Although this particular publication of the present assignee relates to the use of an interferometric temperature measurement system for the control of wafer heating, with sensors and feed-back to a controller and temperature monitor, there is no disclosure of the inventive hot plate structure with in situ surface temperature adjustment as described hereinbelow.